1. Field of the Invention
The present invention relates to filtration systems; more particularly the present invention relates to filtration and recovery systems for tar derivatives, particularly creosote.
2. Description of the Prior Art
As is known to the art, the distillation petrochemicals and coal-tars yields a variety of useful products. Of these, the fractionation products of the heavier organics include tars, pitches, and creosotes which is a useful material for the preservation of wood and wood products. This material, "creosote" may be described as a dark grey oily liquid derivative, with a specific density of about 1.06, a flash point of approximately 165 deg. F, and an ignition temperature of about 637 deg. F. The application of creosote by infusion into a wood article such as poles, masts, timbers, and the like which are to be exposed to the effects of weather and climate, is well known to provide the benefit of a longer service life to the article.
A typical process for the infusion of the creosote into an article includes the process steps of immersing the article to be infused in a vessel, or tank containing creosote, sealing the said vessel or tank to pressurize its contents and via the pressurization cause the infusion of creosote into the article so to permeate it completely so that the creosote permeates the fibrous structure of the wood. Afterwards, the article is removed and is ready for use.
While such processes provide useful methods for the treatment of articles, the steps of immersion and permeation under pressure frequently results in the loosening of debris, wood sugars, fibers, and other impurities from the wood being treated and the entrainment of the same within the creosote which limits the further utility of the creosote in the vessel or tank for further wood treatment. The use of creosote containing such debris, wood sugars, fibers etc. is undesirable as such materials have a tendency to adhere to the surface of an article and form a layer or coating of such impurities which is highly undesirable.
Simple filtration of creosote containing undesirable impurities is often ineffective as the creosote is highly viscous and difficult to pass through conventional filter media. Additionally, simple filtration of an impure creosote require the frequent replacement of filters as the entrained impurities are known to rapidly clog the filter media and substantially decrease the flow of the creosote through the filter medium.
In an alternative method known to the art, creosote containing such undesirable impurities may be distilled in a distillation column, or otherwise fractionated so to separate the creosote from undesirable impurities.
In light of the present level of the art, and of the desirable characteristics of the use of creosote as a wood preservative material, it should be apparent that there remains a continuing need in the art for improved processes for the filtration and purification of creosote, as well as improved filtration apparatus for effecting such filtration and purification.